As CM is completely disregarded.. and mortgages are not paid (well they can be but it's complicated and a loan.. and only available after a substantial amount of time.)
It's a real no brainier. He pays the mortgage amount to you as CM , you pay the mortgage.
He doesn't lose his interest in the house. Because you and he were /are married.
You aren't penalised for having excess income.
When /if the house is sold . The division must include the fact that he should be paying a minimum maintenance for the children. So many men think they are being super smart to pay the mortgage rather than CM because they will use the argument that their 'interest ' in the property has continued because they have been paying.. thus the mortgage payment is an 'investment' whereas CM is a cost with no return .
It's a really shit deal to have him dress it up as mortgage payments but it does depend upon how much it is and how much CM you are due.
For example if the mortgage is £800 a month and his CM liability is £500 then yes he can claim that he's contributed to the mortgage to the time of £300 per month. However if CM on his salary is £700 a month and mortgage is £500 .. then the answer is no. Pay my child maintenance and I will take care of the mortgage but your 'investment' into the property will have ceased.
The only way he can continue with an interest in the property is to pay some or all of the mortgage AFTER he has paid his legal non refundable support for his children.
My best friend had this exact scenario. He paid half the mortgage. But no CM. She paid the other half. They divorced and she remained in the house. Kids got to 18 house was sold and he got half.. as he had contributed half . He could prove this by showing direct payments of half the mortgage. He ended up with 50% of the property. She didn't claim CM . Which would have cost him £5-700 per month for 8 years!
I tried to explain this but she was so scared of losing her home , had no funds for a lawyer, and no confidence he would pay CM (self employed) .. she lost nearly £250k in maintenance.
Please don't do this! .